Latest TCS Aptitude Question SOLUTION: 14. Which is the maximum value of x3y3 + 3 x*y when x+y = 8? a. 4144 b. 256 c. 8192 d. 102

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(#M40019914) TCS Logical Reasoning question Keep an EYE

14. Which is the maximum value of x3y3 + 3 x*y when x+y = 8?
a. 4144
b. 256
c. 8192
d. 102

Asked In TCS juhe rawat (10 years ago)

Unsolved Read Solution (10)

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Read Solution (10) :

himanshu Gupta  (10 years ago)

Answer is a. 4144
You can use AM>=GM
x+y/2 > sqrroot(xy)
4>sqrroot(xy)
16>xy

x3y3=4096
3xy=48
adding them we get =4144

Is this solution Helpfull? Yes (50) | No (7)  

yanna raskala  (10 years ago)

In questions where sum is constant is given and then maximum value has to be found out... then we divide that constant sum in equal parts and put its value in the required equation......


x+y=8
x=8/2
y=8/2
put in equation

(4^3*4^3)+3*4*4=4144

Is this solution Helpfull? Yes (38) | No (6)  

deepak kumar  (10 years ago)

a)4144.
value of expression will max when x=y.

Is this solution Helpfull? Yes (35) | No (1)  

Sujithra  (9 years ago)

we have totally 5 possibilities for x+y=8,
0,8 1,7 2,6 3,5 4,4
highest value will be given when we choose the highest number for both x and y so choose 4,4 sub in x^3*y^3+3x*y thn u will get 4144

Is this solution Helpfull? Yes (9) | No   

sandeep kumar  (9 years ago)

X+Y=8 (MAX. CASE IS X=Y)
X=Y=4
SO. 4^3*4^3+3*4*4=4144 (ANS)

Is this solution Helpfull? Yes (6) | No (1)  

pavan kumar  (8 years ago)

x=8-y
sub x in given eq: (8y-y^2)^3+3(8y-y^2)
differentiate wrt y: 3(8y-y^2)^2*(8-2y)+3(8-2y)
to find out max we equate above eq to zero:(8y-y^2)^2+3=0;8-2y=0
one eq cant be zero then other eq gives y=4
given eq is max when x=y=4
sub x=y=4 in given eq: (4*4)^3+3(4*4)=4144
ans:a

Is this solution Helpfull? Yes (3) | No   

Somanka Dey  (7 years ago)

We have to maximize the value..So here x3y3 + 3 x*y will be maximum if x=y.So x+y=8.
x=4=y.
value=(4^3*4^3)+3*4*4=4144

Is this solution Helpfull? Yes (1) | No   

ayushi garg  (10 years ago)

ans is 24

Is this solution Helpfull? Yes | No (21)  

kokila  (6 years ago)

ans is 102

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ZEEL BUDHBHATTI  (5 years ago)

Value of expression will be maximum when: x=y
so, x=8/2=4 and y=8/2=4.
Putting these values in given equation,
((4)^3*(4)^3)+3(4)(4) = 4144

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